M.T. Lozano

Immunocytochemical and ultrastructural characterization of the cell types in the adenohypophysis of Sparus aurata L. (Teleost)

The structure and immunocytochemistry of the adenohypophysis of sexually mature male specimens of Sparus aurata (gilthead sea bream) were studied. The adenohypophysis was composed of rostral pars distalis (RPD), proximal pars distalis (PPD), and pars intermedia (PI). In the RPD the prolactin cells were organized into follicles which occupied a very reduced area as corresponds to that in saltwater fishes; the corticotropic cells were surrounding the pars nervosa branches and the prolactin follicles. The PPD showed somatotropic, gonadotropic, and thyrotropic cells. The somatotropic cells were isolated, clustered, or surrounding the pars nervosa branches. Only one polymorphic cell type of gonadotropic cells was found in the PPD ventral and dorsal areas and around the PI. The PI was composed mainly of melanotropic cells and a PAS-positive cell layer adjacent to the neurohypophysis. The ultrastructure of the presumptive endocrine cells was reported and their distribution was discussed in relation to those of other teleosts.

The endocrine cells in the gut of Mugil saliens Risso, 1810 (Teleostei): An immunocytochemical and ultrastructural study

The endocrine cells in the gut of Mugil saliens Risso, 1810 (leaping grey mullet) were investigated by immunocytochemical and electron microscopic techniques. Gastrin-, glucagon-, and somatostatin-immunoreactive cells were identified in the cardiac and cecal stomach regions, located mainly in the lower part of the gastric folds and in the upper part of the glands. Substance P-, somatostatin-, and pancreatic polypeptide (PP)-immunoreactive cells were found between epithelial cells in the pyloric stomach region. Gastrin-, cholecystokinin (CCK)-, gastric inhibitory polypeptide (GIP)-, substance P-, Met-enkephalin- and PP-immunoreactive cells were observed throughout the intestine while only the last three of these appeared in the posterior intestine. Nine types of gastroenteroendocrine cells were ultrastructurally characterized; some of them were related to the cell types immunocytochemically identified.

Pancreatic endocrine cells in sea bass (Dicentrarchus labrax L.): I. Immunocytochemical characterization of glucagon- and PP-related peptides

PP-, PYY-, and glucagon-immunoreactive cells were immunocytochemically identified in the pancreatic islets of Dicentrarchus labrax (sea bass). PYY cells also reacted with anti-PP serum. The specificity control showed that preabsorption of PP antiserum by PYY peptide abolished the immunostaining, while the reaction did not change when the PYY antiserum was preabsorbed by PP. These results suggested the existence of a PP/PYY molecule in the sea bass islets. The islet distribution of PP/PYY-immunoreactive cells differed markedly. Thus, in the principal islet and some intermediate islets few PP/PYY-immunoreactive cells are present (type I islets), whereas in the smaller and some intermediate ones they are numerous (type II islets). Adjacent sections stained by peroxidase-antiperoxidase (PAP) technique and individual sections stained by immunofluorescence double staining showed the coexistence of glucagon and PP/PYY-like immunoreactivities. Both islet types contained cells with PP/PYY coexisting with glucagon peptide, while cells showing solely glucagon immunoreactivity were found in type I islets only.

Pancreatic endocrine cells in sea bass (Dicentrarchus labrax L.) II. Immunocytochemical study of insulin and somatostatin peptides.

Insulin (INS)- and somatostatin (SST)-immunoreactive cells were demonstrated by light immunocytochemistry in the endocrine pancreas of sea bass (Dicentrarchus labrax). INS-immunoreactive cells were identified using bovine/porcine, bonito, and salmon (s) INS antisera; the immunostaining was abolished when each antiserum was preabsorbed with its respective peptide but not with unrelated peptides. These cells also reacted with mammal (m) SST-28 (4-14) antiserum. The immunoreaction did not change when this antiserum was preabsorbed by bovine INS. INS-immunoreactive cells were located in the central part of the endocrine areas of the principal, intermediate, and small islets. Two SST-immunoreactive cell types (D1 and D2) were revealed. D1 cells, immunoreactive to SST 14 (562) and sSST-25 antisera, were located next to the glucagon-immunoreactive cells in the peripheral part of the endocrine areas. D2 cells, immunoreactive to SST-14 (562), SST-14 (566), and mSST-28 (4-14) antisera, were found in apposition to the INS-immunoreactive cells. The specificity controls showed that D1 cells expressed sSST-25-like peptides, while D2 cells might contain SST-14 and/or mSST-28-like peptides. The close topographic association between the different SST-immunoreactive cells and both glucagon- and insulin-immunoreactive cells might indicate the existence of a specific paracrine regulation of each endocrine cell type in the sea bass endocrine pancreas.

Endocrine pancreas of Testudo graeca L. (Chelonia) in summer and winter: an immunocytochemical and ultrastructural study

Insulin-, glucagon-, somatostatin-, and PP-immunoreactive cells were identified immunocytochemically using antisera raised against mammalian hormones in the pancreas of Testudo graeca in both winter and summer. The endocrine cells were present throughout the gland, forming scarce islets except in the splenic region. The insulin cell islets were larger and more numerous in the splenic region than in the duodenal one. Winter glucagon-immunoreactive cells were found mainly in isolation while the summer ones occurred in groups which showed no immunoreactive central area; in both seasons these cells were more numerous in the splenic region than in the duodenal one. Somatostatin-immunoreactive cells were found isolated or grouped together more frequently in the splenic region in the summer specimens. No PP-immunoreactive cells were found in the splenic region, although they were numerous and isolated in the duodenal zone. Four cell types (B, A, D, and PP cells) were ultrastructurally characterized by the shape, size, and electron density of their respective secretory granules. Certain ultrastructural differences were detected in the summer and winter endocrine pancreatic cells. In summer specimens a fifth cellular type was observed. The presence of B, D, and PP cells among the epithelial pancreatic duct cells may confirm the comparatively primitive organization of the T. graeca endocrine pancreas.

Identification of two somatostatin-immunoreactive cell types in the principal islet of Sparus auratus L. (Teleostei) by immunogold staining

Two types of somatostatin (SST 14)-immunoreactive cells are identified by immunogold staining in the Lowicryl-embedded principal islet of Sparus auratus: D1 cells, having large moderate to low electron dense granules, located between A cells in the islet periphery and D2 cells, containing smaller electron-dense granules, present between B cells in the central region of the islet. Although SST 28-like immunoreactivity was not observed in D cells of S. auratus, the presence of SST 14 and a SST 22-,25-, or 28-like sequence in D2 and D1 cells, respectively, is discussed. A third SST 14-immunoreactive cell, found in the islet periphery, showed immunoreactive D1- and unreactive A-like granules. This cell type, which has a pyknotic-like nucleus and a dark appearance in osmicated Epon-embedded tissue, is supposed to be the product of fusion of D1 and A cells.

Somatostatin 14- and somatostatin 25-like peptides in pancreatic endocrine cells of Sparus aurata (Teleost): A light and electron microscopic immunocytochemical study

An immunocytochemical investigation demonstrates the presence of somatostatin (SST) 14- and salmon somatostatin (sSST) 25-like peptides in two populations of somatostatin (D) cells in the islets of gilthead sea bream (Sparus aurata). Both cell types were identified by their differing immunoreactivities to the somatostatin antisera used. D1 cells in the islet periphery between glucagon cells showed sSST 25-like immunoreactivity and contained large moderate to low electron-dense granules. D2 cells, present only in the central region of the islets between insulin cells, were immunoreactive to the SST 14 antisera and had smaller electron-dense granules. In S. aurata, as in other teleosts, preprosomatostatin I and II are probably synthesized and processed to SST 14- and sSST 25-like peptides, respectively, in different D cell types.

Comparative study on the endocrine cells in the pancreas of Mauremys caspica (chelonia) in summer and winter.

Four endocrine cell types were identified using peroxidase-antiperoxidase (PAP) technique and ultrastructurally characterized in the pancreas of Mauremys caspica in both winter and summer. In winter, insulin-immunoreactive cells were more abundant and the cell groups larger in the splenic than in the duodenal region, whereas in summer, medium or small cell groups were evenly distributed. Glucagon- and somatostatin-immunoreactive cells were found throughout the gland; they were more numerous in the splenic than in the duodenal region. Polypeptide pancreatic (PP)-immunoreactive cells were found only in the duodenal region. Somatostatin-immunoreactive cells were mainly isolated in winter and grouped in summer. Glucagon- and PP-immunoreactive cells had a similar arrangement in both seasons. Somatostatin- and PP-containing cells showed cytoplasmic processes and could be found next to the pancreatic ducts; the latter were also observed near insulin-immunoreactive cells. Some large secretory granules and numerous, isolated and long rough endoplasmic reticulum (RER) cisternae were seen in winter B cells; in summer B cells numerous lysosomes and few, dilated RER cisternae were found. Summer A cells showed well-developed, dilated RER cisternae and numerous vacuoles; secretory granules were more numerous in winter A cells. In winter B cells and summer A cells some nuclear filamentous inclusions were observed. Few RER cisternae were observed in winter D cells and many in summer D cells; secretory granules were found, the shape and electron density of which differed with the season. PP cells were characterized by their small secretory granules, which were less numerous in winter than in summer, being clustered at the cell pole or dispersed in the cytoplasm, respectively; in winter, the well-developed RER cisternae were dilated and irregularly distributed.